This invention relates generally to molds, and more particularly to a mold cavity structure for the molding of flexible needlepoint sheets used in the craft of needlepoint.
Needlepoint sheets of flexible plastic material which have a plurality of aligned rows of perforations which define plastic threads therebetween are commonly available on the market for those interested in the craft of needlepoint. Thread-like material such as yarn is sewn onto the sheets through the perforations in a desired pattern to form a resultant artistic work. Generally, the plastic threads of the needlepoint sheet which are defined between the perforations therethrough have a rounded cross-sectional configuration.
The difficulty lies in the molding of these plastics sheets with conventional injection mold techniques. Generally, the injection molds utilized have engageable top and bottom mold body halves with open uniform mold channels formed in each half in a lattice configuration wherein the channel lattices of the mold halves cooperatively mate with each other upon engagement of the mold halves to define a mold cavity therebetween for molding a needlepoint sheet of plastic material which is injected into the mold cavity. Many manufacturers of such plastic needlepoint sheets desire a round cross section for the plastic cross threads making up the sheets, as some needlepoint artists prefer this configuration. However, when molding such sheets, a number of critical and troublesome problems are encountered. When the mold halves are separated, portions of the molded sheet will stick to one mold body half or the other, instead of all of the molded sheet remaining seated in the ejection half of the mold which contains the ejection pins for ejecting the molded sheet from that side of the mold.
Also, when the ejection pins on the ejection side of the mold are activated to eject the molded sheets from the mold half, the molded sheet tends to cling to the mold and the ejection pins have a tendency to penetrate and thereby destroy the warm molded sheet instead of ejecting it from the mold channels.
A further problem is encountered in that very often the mold halves, and particularly after continued use and wear, will become slightly offset with each other or mismatched thereby creating undesirable mismatched offsets in the cross section of the threads of the resultant needlepoint sheet being molded, giving it a poor appearance and making the perforations smaller than desired.
It is a principal object of the present invention to provide a mold for molding needlepoint sheets of flexible plastic material which is devoid of the aforementioned disadvantages encountered in the molds of the prior art.